The present application claims priority to Japanese Application No. P2000-236471 filed Aug. 4, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to an electrolytic polishing apparatus, an electrolytic polishing method and a wafer subject to polishing, and more specifically, to an electrolytic polishing apparatus, an electrolytic polishing method and a wafer subject to polishing, which permit detection of a termination point in electrolytic polishing.
2. Prior Art
Copper wiring presents lower electric resistance, lower capacity and higher reliability than aluminum wiring and is thus increasing in importance for micro elements dominantly affected by circuit delay due to parasitic resistance and parasitic capacity occurring in the wiring. A damascene method is widely applied as the most popular method of forming copper wiring. In particular, a dual damascene method meets with general acceptance from the viewpoint of manufacturing cost. There is expectation that a process of manufacturing copper wiring by the use of the dual damascene method will be less costly than a conventional aluminum wiring process.
However, since chemical mechanical polishing (which will be hereinafter referred to as CMP) of copper is considered to be a complicated process requiring expensive slurry and pad, a problem in an increase in manufacturing cost is encountered with the CMP. In addition, since the CMP is based on mechanical polishing, not only copper requiring polishing but also an insulating film around the copper is polished to bring about erosion, resulting in a problem in difficulty to achieve flatness of a wiring layer. The CMP further finds difficulty in detecting a termination point and therefore presents problems like over-polishing and under-polishing. As a result, there are problems in that the CMP causes excessive dishing or inter-wiring short circuit.
An attempt to form a dual damascene structure by polishing copper by means of electrolytic polishing is now being made for the purpose of solving the problems mentioned above.
On the other hand, in electrolytic polishing, a quantity of polishing is decided on the basis of a polishing time. For that reason, an operator finds difficulty in ascertaining a point of time desired to terminate polishing, that is, a termination point of polishing, resulting in problems in that over-polishing or under-polishing occurs depending on variations in thickness of a film subject to polishing, changes in electrolytic polishing conditions or the like.
An electrolytic polishing apparatus according to a preferred embodiment of the present invention performs electrolytic polishing of a conductive film subject to polishing formed on a substrate and includes a resistance measuring unit for measuring resistance of the film subject to polishing. The electrolytic polishing apparatus also includes a termination point detecting portion for detecting a termination point of polishing by reading a variation of a resistance value measured by the resistance-measuring unit. The electrolytic polishing apparatus further includes a polishing control portion for terminating electrolytic polishing on the basis of the termination point of polishing detected by the termination point detecting portion.
The electrolytic polishing apparatus includes a resistance measuring unit for measuring the resistance of the film subject to polishing, permitting the measurement on the resistance value of the film subject to polishing varying with the progress of electrolytic polishing. That is, with the progress of electrolytic polishing, the thickness of the film subject to polishing is made smaller, and accordingly, the resistance value measured by the resistance measuring unit increases. When the film subject to polishing is completely removed by polishing, the resistance measuring unit proceeds a measurement of a resistance value of the substrate on which the film subject to polishing is formed, for instance, and as a result, the resistance value reaches a constant reaches a constant value.
The electrolytic polishing apparatus detects the termination point of polishing by reading the variation of the resistance value of the film as described the above with the termination point detecting portion. For instance, a point of time when the resistance value reaches a constant value is detected as the termination point of polishing.
Then, the electrolytic polishing apparatus terminates electrolytic polishing immediately after the termination point of polishing is detected. A process between detection of the termination point of polishing and termination of electrolytic polishing may be automatically performed by using the polishing control portion to terminate electrolytic polishing on the basis of detection of the termination point of polishing.
An electrolytic polishing method according another preferred embodiment of the present invention performs electrolytic polishing of a conductive film subject to polishing formed on a substrate and includes the step of detecting a termination point of electrolytic polishing to terminate electrolytic polishing by detecting a variation of electric resistance of the film subject to polishing in the process of electrolytic polishing.
The electrolytic polishing method detects the variation of resistance of the film subject to polishing in the process of electrolytic polishing. That is, with the progress of electrolytic polishing, the thickness of the film subject to polishing is made smaller, and accordingly, the resistance of the film subject increases. When the film is completely electrolytic-polished, the electrolytic polishing method proceeds to measure of a resistance value of the substrate on which the film subject to polishing is formed, for instance, and as a result, the resistance value reaches a constant value. For instance, the time when the measured resistance value reaches a constant value is set as the termination point of polishing. The electrolytic polishing method permits accurate detection of the termination point of electrolytic polishing to terminate electrolytic polishing by detecting the variation of resistance of the film subject to polishing as described the above.
A wafer subject to polishing according to another preferred embodiment of the present invention includes a substrate, a first conductive layer formed on the surface of the substrate, a terminal connection area connected with terminals of a resistance measuring unit and formed on the surface-side periphery of the first conductive layer and a second conductive layer subjected to electrolytic-polishing selectively to the first conductive layer and formed on the surface of the first conductive layer except for the terminal connection area.
According to the wafer subject to polishing, since the terminal connection area is formed on a surface-side periphery of a first conductive layer, a resistance varying according to polishing of a second conductive layer can be measured by, for instance, connecting the terminals of the resistance measurement unit to the portions of the terminal connection area facing each other within a plane of the wafer subject to polishing. Then, when the second conductive layer is removed by means of electrolytic polishing, the thickness of the conductive layer portion is reduced, and accordingly, the measured resistance value increases. When the second conductive layer is completely removed from the first conductive layer by means of electrolytic polishing, the resistance measuring unit proceeds to measure only the resistance of the first conductive layer, and as a result, the resistance value reaches an approximately constant value, regardless of the continuation of electrolytic polishing. For instance, a period of time when the resistance value reaches a constant value is set as the termination point of electrolytic polishing of the second conductive layer, resulting in detection of the termination point of electrolytic polishing.